Enter means literally "to go inside of," as one would enter a building, not an ethereal or abstract concept.
Paul says, "Flesh and blood cannot inherit the kingdom of God" (I Corinthians 15:50), which agrees perfectly with Jesus' statement. When combined with Jesus being the pattern for the entire new creation, and that He did not go through a conversion process and yet was born again by a resurrection from the dead, John 3:3-8 must refer to the end of the process.
Otherwise, we have to try to explain away verses like "That which is born of the flesh is flesh" (verse 6). It is perfectly clear on its own; it needs no explanation. We are still confined to the earth. But the birth Jesus is speaking about occurs later: "That which is born of the Spirit is spirit"!
The old "hat pin test" still works. We still bleed and feel pain. We are still flesh. We are not spirit yet, so we have not been born again.
It becomes even clearer:
Do not marvel that I said to you, "You must be born again." The wind blows where it wishes, and you hear the sound of it, but cannot tell where it comes from or where it goes. So is everyone who is born of the Spirit. (verse 7-8)
If we—proven to be fleshly beings—can still see each other coming and going, we are not yet spirit. It is so plain!
The process that ends in being born again begins at begettal. Throughout the entire process, however, there are types, symbolic actions, that represent later realities. Repentance and baptism typify a death (Romans 6:2-11). We have died to sin, and when a person dies, he is buried. Likewise, we are buried in water and are raised up out of it (typifying a resurrection) to begin a new life.
But we are not born again yet; we are still flesh and blood. God imparts His Spirit to us at the laying on of hands, but we are not spirit. We have the Spirit in a small measure as a down payment, an earnest, a guarantee, of our future, complete endowment (II Corinthians 1:22; 5:5). It has begotten us to begin the process.
We go through these types but the reality is still future. And it will not occur until we literally die, our bodies decay, and we are resurrected by the power of God. Only then will we be spirit. Then we will be like the wind. The process will have been completed. We will be born again!
